The present invention generally relates to a tape driving apparatus for controlling the transportation of a tape medium by a supply reel and a winding reel.
In recent years, a highly efficient tension control art which prevents tape damage has been demanded, because of the use of thinner tapes in the tape driving apparatus. Also, the tape driving mechanism is also simplified with the demands for smaller size, lighter weight, thinner size of the apparatus being provided. Therefore, the tape driving apparatus is provided which is simplified in mechanism without provision of the tension detecting sensor of the tape.
The conventional tape driving apparatus (hereinafter a VCR will be described as a representative by way of example) is shown in, for example, Japanese Patent Application Publication Tokkaisho No. 60 - 163258.
The conventional tape tension controlling method will be described hereinafter. The conventional tape tension controlling method is to constantly control the tape tension by the application, upon the supply reel diameter, of a back torque proportional to the supply reel diameter. The principle thereof will be described. The formula is as follows EQU STSN.times.Rs=Qs (1)
wherein STSN: tape tension in supply reel
R2: supply reel radius PA1 Q2: supply reel motor torque
Therefore, it has been determined that the torque proportional to the supply reel diameter has only to be applied to the supply reel motor in order to retain the tape tension STSN constant when the tape is transported at a constant speed.
But the above described construction has the following problems. Namely, the VCR has not only the modes of the recording, and the normal reproduction, but also the operation modes called jog and shuttle. The tape speeds except for the tape speed at the normal reproduction time exist, with the tape acceleration and deceleration being repeated. At this time, in the method of applying the torque proportional to the above described supply reel diameter, the tape tension may be retained constant under the conditions where the tape is transported at the constant speed, with the fluctuations of the dynamic tension to be caused by the acceleration and the deceleration of the tape being impossible to be suppressed. In the conventional tape driving apparatus, the acceleration/deceleration responses are delayed in the acceleration/deceleration of the tape so as to reduce the fluctuations of the tension. Therefore, the transportation of the tape to the object point of the tape is delayed so as to sacrifice the access property of the tape.
The tape driving apparatus to be used for the external memory apparatus of the computer will be described hereinafter in the conventional embodiment. In the tape driving apparatus described in Japanese Patent Publication Tokkosho No. 59-20178, the current for driving the reel motor is divided into three components such as acceleration current, tension current, drag current in the acceleration and the deceleration of the tape. The reel radius and the inertia are detected, and the tape acceleration speed is obtained from the target speed to be controlled, the present tape speed and the tape acceleration from the enacted time, with a method of computing, setting the driving current of the reel so that the tape tension may become constant.
But in the above described construction, the tape running loads changes with the changes in environment where the tape driving apparatus is provided, with the aging, the drag current component does not become constant, with a problem that the tape tension has been changed. In order to correct the problem, a tension detection sensor is provided. Accordingly the requirement of the tape tension sensor interferes with the smaller size and the lighter weight of the apparatus.